The search for both light-weight and strong structures has been ongoing for many centuries. Known support structures come in different shapes and forms with some providing certain strength and weight advantages. However, the strength and weight advantages of known structures typically come with a heavy price tag; that is, the increased strength and lower weight of the structure in certain aspects of the structure are obtained by lowering the strength in other aspects of the structure. These tradeoffs typically limit the applications of known structures, or require modifications or duplications that function to increase weight of the structure.
In performing research for a new vehicle, the issue of energy efficiency is of paramount concern. Key features include an aerodynamic design for high speed with a low rolling resistance, meaning the need for a relatively small down force (e.g., low mass). The desire was for a vehicle that could travel faster than 100 km/h with a weight of less than 24 kg. With such a low weight, however, safety concerns were raised for passengers if the vehicle were to strike a non-moving object. The need then for an ultra-light weight yet very strong structure was needed.
Existing space truss structures are often based on plane truss structure that is not optimal for space truss structure. Plane truss structures such as Pratt, Howe, Warren, Baltimore and Fink (J. L. Meriam, L. G. Kriage, “Engineering Mechanics STATICS”, #5 Chapters 3 and 4, published by Wiley, 2003) have inefficient bar lengths especially if beam diameter is the same throughout the structure. Non optimized beam diameter can unnecessarily increase the mass of the structure or result in a weakened structure. A misplaced beam can cause the structure to be unbalanced providing weak or redundant structural points.
Many known structures are based on designs that incorporate rectangular supporting shapes that are easy to build, but do not have good interconnection of the beams. Alternatively, more advanced structures use triangular shapes for reinforcing the structure. These two-dimensional (“2D”) elements are typically not connected in a pattern or bar length that is optimal. Likewise, the connections that are utilized typically do not achieve optimal peak performance.
A W-shaped (corrugated) structure 10 as illustrated in FIG. 1 is known and generally provides effective strength characteristics in two directions (i.e., in X-Y-Z rectangular coordinates, it is strong if the force vector is in the Y and Z axes, but it is weak if the force vectors are in the X axis direction). So while the W-shaped structure 10 provides good 2D strength characteristics, it presents very poor three-dimensional (“3D”) strength characteristics. Accordingly, the W-shaped structure 10 has more of a tendency to buckle because of the relatively thin walls and has a double buckling direction, which make this structure a good single energy absorber, but not usable for dynamic loads.
There are known 3D structures, however, many of the 3D “lightweight” structures have weaknesses that severely limit their use. One example of a structure that utilizes a tetrahedron is disclosed in U.S. Pat. No. 3,220,152 entitled, “Truss Structure” by R. G. Sturm (“the '152 patent”). However, while the '152 patent does disclose multi-directional connections as illustrated in FIG. 3, the disclosure is limited to simple triangular interconnections, such that the anti-buckling characteristics of the structure are not optimized, which again limits the effectiveness of the structure.
Another known design is the “honeycomb” structure 20 as illustrated in FIG. 2. While this design does provide for a relatively strong structure, the strength characteristics are not equally multidirectional. In other words, the structure is not equally strong in each of the X, Y and Z axes. Additionally, another drawback to the honeycomb structure 20 is that it is too heavy for its volume to be considered light weight, which also functions to limit its use.
Another known structure is the Icosahedron, which is a polyhedron with twenty faces or sides. However, the Icosahedron can only be provided as a single piece and therefore cannot be provided as a continuous structure.
So then, the various issues faced with known structures are that they are typically designed to be strong for a specific force vector, meaning that they function well in one axis but not in another different axis. Such structures are not multidirectional and therefore have limited use. Additionally, known structures are often made with many different length and diameter beams thereby making production complex.